Along with getter methods, we can also create setter methods which reassign values of existing properties within an object. Let’s see an example of a setter method:

const person = { _age: 37, set age(newAge){ if (typeof newAge === 'number'){ this._age = newAge; } else { console.log('You must assign a number to age'); } } };

Notice that in the example above:

  • We can perform a check for what value is being assigned to this._age.
  • When we use the setter method, only values that are numbers will reassign this._age
  • There are different outputs depending on what values are used to reassign this._age.

Then to use the setter method:

person.age = 40; console.log(person._age); // Logs: 40 person.age = '40'; // Logs: You must assign a number to age

Setter methods like age do not need to be called with a set of parentheses. Syntactically, it looks like we’re reassigning the value of a property.

Like getter methods, there are similar advantages to using setter methods that include checking input, performing actions on properties, and displaying a clear intention for how the object is supposed to be used. Nonetheless, even with a setter method, it is still possible to directly reassign properties. For example, in the example above, we can still set ._age directly:

person._age = 'forty-five' console.log(person._age); // Prints forty-five



Currently, in robot there is a getter method for numOfSensors but no setter method! What if we need to add or remove some sensors? Let’s fix that problem.

Add a setter method named numOfSensors using the set keyword. Provide a parameter of num. Leave the function body empty for now.


There are a couple of things we should do in the setter method:

  • Add a check to see if num is a number using the typeof operator.
  • num should also be greater than or equal to 0.
  • If both conditions are met, reassign this._numOfSensors to num.

Now add an else that logs 'Pass in a number that is greater than or equal to 0' to the console.


Use the numOfSensors setter method on robot to assign _numOfSensors to 100.


To check that the setter method worked, console.log() robot.numOfSensors.

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